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(According to this Module) Birdsong is...

complex courtship signal involving variation in auditory frequencies with different intensities over time. Controlled by a series of circuits that all lead to the control of a bird's motor neurons. Sexually driven Birdsong also leads to sexual dimorphism.

When is birdsong learned?

at the developmental age.

[Roberts did not clarify if this was during all types of bird learners or just some] I think the main point is, the developmental age is important for building the blueprints of the anterior pathway.

How does birdsong change in the course of an individuals life?

seasonal variation
auditory input
feedback instruction (feedback says whether this song worked or not. Which leads to differences controlled by the fact that when it works more testosterone is released from gonads making males "cocky")
sex differences- sex steroids!

[no clarification on what type of learners this is for, Personal Assumption: Works for variation on seasonal learners, for all new songs on open ended learners, and does not effect age-limited learners after developmental period)

Neurons communicate via...

chemical transmission between units (cells) of a circuit\

activation potential sent to pre synaptic area and Ca channels shoot Ca2+ ions in the presynaptic area causing neurotransmitters to be released into synapse and attach to channels on the post synaptic area of next neuron and pass the signal along

How do Neurons interact with one another

Cell body/dendrites receive input from other neuronal systems and “integrate” that to decide (do you reach the threshold potential?) if the neuron will fire

What are the steps that happen at the synaptic dendrites? (think diagram)

1.) Action potential arrives; triggers entry of Ca2+
2.) IN response to Ca2+, synaptic vesicles fuse with presynaptic membrane, then release neurotransmitter
3.) Ion channels open when neurotransmitter binds; ion flows casue change in postsynaptic cell potential.
4.) Ion channels will close as neurotransmitter is broken down or taken back up by presynaptic cell

In order to create bird song, brain needs input on...

Time of year (light)?
Sufficient food?
What do I already know?
What sex am I?

Common features between bird and mammalian nervous systems

In birds the cerebrum is organized into large cell clusters, whereas only the lower portion of the cerebrum is as subdivided as in mammals

Other common features of reptiles, birds, and mammals: all have similar structure of the brain consisting of the spinal cord within the vertebral backbone, , the hindbrain in front of it, the midbrain, the thalamus, and the cerebrum (with the cerebellum).

What was wrong with the classical view of a bird's brain.

The classical view held that these gross structural differences meant that reptiles and birds weren’t as intelligent as humans, and that these large cell clusters could not be responsible for “higher learning”.

now We know that there are completely homologous functions in the large cell clusters of the avian forebrain and the mammalian cerebral cortex.

The complexity of the brains structure is not related to behavioural complexity, but more to the size of the animal. i.e. small bird=less physically complex, but not less not less behavioural complex

Bird song is based on

A Basic Neural Circuitry

with multiple connections (circuits!) and inputs with final connections to the vocal organs and respiratory system. (picture in lecture)

HVC =

Hyperstriatum Ventrale pars Caudale or High Vocal Center

the the first step in the circuits of both the anterior and posterior pathways.

Interacts with estradiol, because HVC deals with neurogenesis.

RA =

Robust nucleus of the Acropallium

heart of bird song, the size of this region is directly correlated with the strength, complexity, and volume of bird song.
It can shrink and expand during a year, because of need or lack of need to sing. HVC controls the sending of new neurons to RA region.
Also a source of sexual dimorphism in birds.

DLM =

Dorso- Lateral division of the Medial thalamus

necessary for learning in all birds

lMAN =

lateral Magnocellular nucleus of the Anterior Neostriatum (IMAN=LMAN, he writes it both ways)

Lesioning LMAN, located in the anterior forebrain pathway in young birds disrupts song production.
Lesioning LMAN on an adult bird shows no effect.
Lesioning LMAN on an adult canary (an "open-ended learner" species, which can learn songs later in life) shows a progressive deterioration of song.

Area X

necessary for song learning in all birds

discovered that the neurons that project from the HVC to Area X are highly responsive when the bird is hearing a playback of his own song.

When each of these anterior pathway elements legioned what happens?
1.)Area X
2.)IMAN

Area X: When lesioned during sensitive phase, song never crystallizes
lMAN: When lesioned during sensitive phase, song rapidly becomes stereotyped and nothing new can be learned

A neural network like that that creates birdsong is comprised of:

Multiple neurons, connecting from one to the other, each bringing in different elements of information to elicit a response from a final common path

How is Birdsong sexually dimorphic?

The overall effect is that men have larger RA regions (where birdsong is developed)

but caused by the dimorphism in hormone amount and concentration sent to the brain (estradiol and DHT)

Three emphasized Categories of chemical signals in animals

Endocrine signals: hormones carried between cells by blood or other blood fluids
Neural Signals: diffuse a short distance between neurons
Neuroendocrine signals: Are released by neurons but act on distant cells

other signals: Autocrine Paracrine Pheromones

What are hormones?

Hormones are chemical signals that circulate through bodily fluids and affect distant target cells; similar concept in brain except chemicals are “delivered” to their target cells

What are hormone receptors?

Receptors are proteins that bind to a particular signal and change confirmation or activity in response. (vary because of several different possibilities of Splicing.)

in order to regulate positive regulation of a firing signal.... (How do you control the firing of a hormone?)

you need feedback inhibition. example the production of the hormone cortisol sends a message back to the pituitary gland saying that it has produced x amount of cortisol already and down regulating its production.

Ways in which hormones can act on the Traditional pathways of hormone action, the nucleus of the axon (site of transcription):

In females dihydrotestosterone is not able to be crearted from testosterone in turn it does not allow for females crystallization of bird song.

Personal Assumption: Because of a lack of input of testosterone from females (they don't have enough for extracurricular functions like development of elaborate bird song) their is a lack of converter enzymes due to their lack of necessity. Is it an adaption over a females life, or are they more this way?)

Different ways that Hormones are Released and Transported. (ehh... vague)

Since steroids are lipid soluble, they can pass right through cell membrane (peptide hormones/neurotransmitters are stored in vesicles & then released)
They are also carried in bloodstream by binding proteins to make them more soluble in plasma, but tend to store in fat deposits around body!

In what ways are T levels increased in adult males?

-Territorial males have higher levels of T than non-territorial males. (Can be increased within 10 min. of territory take over)

Differences in sex chromosomes lead to gonadal differentiation
Ovaries & testes express different levels of steroid hormones, areas in the brain express different levels of steroid receptors & aromatase activity
Brain nuclei in song system grow in males, not in females; at the same time, males learn to sing
In adulthood, song behavior is activated in males, but not in females, through steroid hormones

Biological Rhythms

Daily- circadian
Seasonal- annual

Longer variations based on weather cycles, environmental pressures (wet in winter and dry in summer)
But for birdsong, seasonal is more “important” -->because there is no point in singing when there are no girls looking.

the melanopsin then DEPOLARIZES w/light (like a normal neuron, unlike cones and rods)--> the ion cells then send message of day length to hypothalamus nucleus which compares the amount of light input to the stored 24 hour molecule clock.

Explain Circadian Rhythm in birds...

eyes see the dawn coming and then start to make steroid and create a new song and then after practicing and learning it they sing with pride.

This process is integrated over time in the brain in a yearly time scale

Environmentally determined cyclical changes, such as changes in daylight, temperature, and availability of food, serve primarily to refine and adjust physiologically determined circadian or circannual rhythms: in the absence of external cues, the internal rhythms gradually drift out of phase with the environment.

What is SCN biological clock based on?

a molecular clock, that has evolutionarily been sent to a 24 hour period.

So how does the body store memory (read Ch 45)?

Through the Brain in a process called long-term potentiation (LTP)

Research on the molecular basis of memory is based on two fundamental ideas:

(1) Learning and memory must involve some type of short-term or long-term structural or chemical change in the neurons responsible for these processes.
(2) It will be much easier for researchers to understand what these changes are if they study an extremely simple system of neurons.

How do synaptic membranes work with LTP?

slides 8-11 on lecture 5

learning stimulates synapses over and over so that they become stronger, gain a larger surface areas, develope more receptors and become more sensitive to a specific input--> memory

So what is LTP?

In general, Long Term Potentiation (LTP) works when something changes in response to repeated stimulation of a particular neuron.

Changes in synaptic transmission are caused by

Events in strengthening synapse in LTP by placing more receptors in the dendrites
Short term differences begin to create long term effects in the animal's hormone production

Key is the activation of kinases, because when the Ca2+ ions are in surplus they activate the kinases which goes on to transcribe more genes that make the synapse more responsive.

Songbird neurogenesis...

Songbirds continuously undergo neurogenesis, replacing dying cells
In this case, the “stem cell” is a modified radial glia!
Migrating neuroblast divides once more as it travels to populate 2 brain areas (old neurons travel to area X and new ones to RA)

ions need to reach a _________________ before the Na channels can open.

threshold of membrane potential

which leads to depolarization and an action potential.

From the mouth of Dr. Roberts, "So all memory is..."

the changing of the strength of the circuitry between a neural system that is set up to record this information.

does not raise action potential, but rather sustains a.p. that in turn strengthens the response.

In the sense of neurons affecting motor function: the RA region of the brain is connected by ____________ to the __________ muscle.

series of circuits (in particular from RA-->DLM-->xNllts-->Syrinx

syrinx

Why Do Birds Sing?

Kin Recognition: Who is in the family?

Species recognition: Who should I mate with?

Neighbor recognition: “Good fences make good neighbors”

Territory marker and mate guarding

Mate selection: Good singers make good lovers i.e. louder, longer, and more complex(Large HVC) means they have good genes, less parasites, and can retrieve food better.

In the production of bird song, the syrinx/nXllts recieve input from RA and HVC,
what about legions?

Lesions of the RA or HVC or their connections produce a deficit in song
The size of the RA is greater and far more important in males then that in females.

What is involved in the process of adult bird neurogenesis (i.e. new neurons being born)

-replace dying cells
-In this case, the “stem cell” is a modified radial glia!
-Migrating neuroblast divides once more as it travels to populate 2 brain areas[old neuron go to Area X and new one goes to RA]

in females the neuron die and are not regenerated as quickly as with males because it is stimulated by the gonads.

the ZENK transcription factor is activated in area X in response to androgen to do what?

ZENK activity works to create genes that work with altered proteins to strengthen synaptic regions in order for the bird to express a perfected song (remember LTP and gene expression!)
Then once crystallized ZENK activity subsides and a permanent neural circuitry is in place. (well maybe only for a season, depending on the type of bird)

age limtied learners

Learn one song once and sing it over and over for the rest of their life (permanent neural circuitry).

What is special about the way that a canary learns its seasonal songs?

Canaries can learn completely new songs every time that their biological clock says its spring, while many learners only create a variation on one song their entire life. (canary=open ended learners)

Gene expression of ZENK also changes

Pre-subsong: ZENK synthesis generally high in many areas (in absence of hearing or practice singing)-learning not really able to practice.

Animals determine that it is April vs October via:
1- Temperature changes outside
2- Determining the period of sunlight in the day
3- Using neuronal magnetic sensors to determine location
4- Using a memory circuit of some form to determine if the day is getting shorter/longer

D- 1, 2 and 4

Birds remember new learned song in part via a mechanism called LTP. What is it?

D- the strengthening of post-syntaptic structures allowing for enhanced transmission of an incoming signal

How do sex hormones aid in the development of birdsong?

A- They cause the genesis of new neurons that play a crucial role in setting up the neural circuit that underlies the song production

What are the Bird Chromosomes?

Males:ZZ Females:ZW

Before hatched, vocal nuclei develop In both sexes due to Z chromosome activity which both males and females share

The Estrogen then binds to HVC receptors, facilitating growth of HVC and connecting nuclei through neurogenesis.

How does a feedback loop work to control song production?

Androgens also stimulate singing in adulthood by binding to vocal nuclei receptors, which in turn enhances testosterone release from gonads, encouraging more singing.

"Yah I am cool now"--> send it back to continue the production of 'cool' hormones

Generally thought that binding to receptors reduces the threshold for electrical activity – i.e. neurons associated with singing are more ready to fire. (This is a general thought not a fact, because in fact the receptors are just more responsive and there is an elongation of action potential not a lowering of threshold potential--K+ channels do not turn off as quickly)